1. Field of the Invention
The present invention relates to an engagement structure for disengageably and rotatably engaging a pair of cylindrical members, such as lens barrels of a camera.
2. Description of the Related Art
In a known engagement structure to connect (or fit) a pair of cylindrical members having different diameters, such as zoom lens barrels of a camera so as to be disengageable from one another in the axial direction and relatively rotatable in the circumferential direction, one of the cylindrical members which is provided with radially extending portions (which will be referred to as projections or engagement projection portions) that are inserted in grooves provided in a flange of the other cylindrical member, so that the engagement projection portions are rotatable in a plane of the flange.
In the above engagement structure, the amount of relative rotation (angular displacement) of the cylindrical members is determined in accordance with the number of the engagement projection portions or grooves. If the cylindrical members have a single engagement projection and a single groove, respectively, the cylindrical members are relatively rotatable over approximately 360 degrees. However, in this engagement structure, the flange is only supported by the single projection and, hence, the engagement is not stable.
To solve this problem, it is possible to provide, for example, three engagement projection portions which are spaced at equal angular pitches (e.g., 120 degrees). An increase in the number of the engagement projection portions, i.e., number of the supporting portions, contributes to a stable relative rotation of the cylindrical members. However, the maximum relative angular displacement is remains at approximately 120 degrees.
In a lens barrel arrangement, it is preferable that the angular displacement of the cylindrical members be as large as possible to increase the axial displacement of the lens at each mode of use and to provide a sufficient angular displacement from a use position to a disassembling position.
Under these circumstances, in an arrangement having three pairs of engagement projection portions A1 through A3 and grooves B1 through B3, as shown in FIG. 25, it is possible to space at least one engagement projection portion A2xe2x80x2 and groove B2xe2x80x2 from the remaining engagement projection portions and grooves at an angular distance different from the angular distance (120 degrees) between the remaining engagement projection portions and grooves, to thereby increase the angular displacement of the cylindrical members, instead of the equal pitch arrangement of the three pairs of the engagement projection portions and grooves.
However, in this solution, the supporting portions are not uniformly distributed, thus resulting in less stability during rotation or less efficiency of assembling and disassembling operations. Moreover, when the cylindrical members are rotated, for example, a first engagement projection reaches the groove for the second or third engagement projection, and the first engagement projection is disengaged at this moment, thus leading to insufficient stability.
To eliminate these problems, in Japanese Kokai Publication No. 11-133285, the engagement projection portions and grooves are disclosed as having different lengths in the circumferential direction and in the radial direction. With this arrangement, the engagement projection portions are allowed to be disengaged only at the corresponding grooves. However, it is necessary for the cylindrical members to have play in the length thereof in the radial direction.
It is an object of the present invention to provide an engagement structure for cylindrical members, which can be made small and in which the angular displacement of the cylindrical members can be increased even if there is no play in the radial length thereof, so that it is difficult to make the length of the engagement projection portions different, the stability of the cylindrical members during rotation thereof can be improved, and the assembling and disassembling operations of the cylindrical members can be easily carried out.
According to an aspect of the present invention, an engagement structure for cylindrical members is provided, including a first cylindrical member including a plurality of engagement projection portions of different shapes having the same projecting length in the radial direction, and a second cylindrical member including a plurality of groove portions corresponding to the engagement projection portions, each the groove portions having at least one groove; wherein one of the first and second cylindrical members is accommodated inside the other of the first and second cylindrical members. The engagement projection portions and the corresponding groove portions can be engaged and disengaged only at one relative circumferential position of the first and second cylindrical members; and at a relative circumferential position other than the one relative circumferential position of the first and second cylindrical members, the engagement projection portions of the first cylindrical member are always engaged with at least a portion of the groove portions other than the grooves thereof.
In an embodiment, the overall lengths of the engagement projection portions in the circumferential direction are different from each other, and the overall lengths of the groove portions in the circumferential direction are different from each other.
In an embodiment, the engagement projection portions and the groove portions are formed so that the overall length in the circumferential direction of each engagement projection portion and groove portion is gradually increased.
In an embodiment, the engagement projection portions, excluding one engagement projection portion, are each provided with a pair of right and left projections which are spaced by a groove in the circumferential direction; and wherein the groove portions, excluding one groove portion, are each provided with a pair of right and left grooves which are spaced by a projection in the circumferential direction.
In an embodiment, the grooves of the engagement projection portions have different circumferential lengths, and the projections of the groove portions have different circumferential lengths.
In an embodiment, the groove portions satisfy the following conditions:
A greater than Bj; 
A greater than Dj; 
A less than Ej; 
Cj less than Cj+1; 
Ej less than Ej+1; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the groove portion having no projection, Bj and Dj designate the circumferential lengths of the grooves of the j-th groove portion, Cj designates the circumferential length of the projection of the j-th groove portion, and Ej designates the overall length of the j-th groove portion.
In an embodiment, the engagement projection portions satisfy the following conditions:
A greater than Bj; 
A greater than Dj; 
A less than Ej; 
Cj less than Cj+1; 
Ej less than Ej+1; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the engagement projection portion having no groove; Bj and Dj designate the circumferential lengths of the projections of the j-th engagement projection portion; Cj designates the circumferential length of the groove of the j-th engagement projection portion; and Ej designates the overall length of the j-th engagement projection portion.
Furthermore, in an embodiment, the following conditions are satisfied:
Bj=Bj+1; and 
Dj=Dj+1. 
In an embodiment, the following condition is satisfied:
Bj=Dj. 
Preferably, one of the cylindrical members is a cam ring which is adapted to move a lens barrel of a camera, and the other cylindrical member is a linear movement guide ring which is adapted to guide a linear movement of a lens support cylinder which is rotatably supported by the cam ring and is moved linearly in an optical axis direction in accordance with the rotation of the cam ring.
In another aspect of the present invention, the grooves of the engagement projection portions are located at different positions.
In an embodiment, the following condition is satisfied:
Ej=Ej+1; 
wherein Ej designates the overall length of the j-th groove portion or the overall length of the j-th engagement projection portion.
In an embodiment, the groove portions satisfy the following conditions:
A greater than Bj; 
A greater than Dj; 
A less than Ej; and 
Bj less than Bj+1; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the groove portion having no projection, Bj designates the circumferential length of a first groove of the j-th groove portion, Dj designates the circumferential length of a second groove of the j-th groove portion, and Ej designates the overall length of the j-th groove portion.
In an embodiment, the engagement projection portions satisfy the following conditions:
A greater than Bj; 
A greater than Dj; 
A less than Ej; and 
Bj less than Bj+1; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the engagement projection portion having no groove, Bj designates the circumferential length of a first projection of the j-th engagement projection portion, Dj designates the circumferential length of a second projection of the j-th engagement projection portion, and Ej designates the overall length of the j-th engagement projection portion.
In an embodiment, the following condition is satisfied:
Ej=Ej+1. 
In an embodiment, the following condition is satisfied:
Cj=Cj+1; 
wherein
Cj designates the circumferential length of the groove of the j-th engagement projection portion or the circumferential length of the projection of the j-th groove portion.
In an embodiment, one of the cylindrical members is a cam ring which is adapted to move a lens barrel of a camera, and the other cylindrical member is a lens support cylinder which is rotatably supported by the cam ring and is moved linearly in an optical axis direction in accordance with the rotation of the cam ring.
In another aspect of the present invention, the engagement projection portions have different numbers of grooves.
In an embodiment, the following condition is satisfied:
Ejxe2x89xa0Ej+1; 
wherein Ej designates the overall length of the j-th groove portion or the overall length of the j-th engagement projection portion.
In an embodiment, the projections of the groove portions have different circumferential lengths.
In an embodiment, the grooves of the engagement projection portions have different circumferential lengths.
In an embodiment, the engagement projection portions and the groove portions of the cylindrical members are arranged so that the overall lengths thereof in the circumferential direction gradually increase.
In an embodiment, the following conditions are satisfied:
A greater than Bj,k; and 
Bj,k greater than Bj+1,k; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the groove portion having no projection, and Bj,k designates the circumferential length of a k-th groove of a j-th groove portion.
In an embodiment, the following conditions are satisfied:
A greater than Bj,k; and 
Bj,k greater than Bj+1,k; 
wherein xe2x80x9cAxe2x80x9d designates the circumferential length of the engagement projection portion having no groove, and Bj,k designates the circumferential length of a k-th projection of a j-th engagement projection portion.
In an embodiment, the following condition is satisfied:
Bj,k=Bj,k+1; 
wherein Bj,k designates the circumferential length of a k-th groove of a j-th groove portion or the circumferential length of a k-th projection of a j-th engagement projection portion.
In an embodiment, the following condition is satisfied:
Cj,k greater than Cj+1,k; 
wherein Cj,k designates the circumferential length of the projection provided between the k-th and (k+1)-th grooves of the j-th groove portion.
In an embodiment, the following condition is satisfied:
Cj,k greater than Cj+1,k; 
wherein Cj,k designates the circumferential length of the groove provided between the k-th and (k+1)-th projection of the j-th engagement projection portion.
In an embodiment, one of the cylindrical members is a cam ring which is adapted to move a lens barrel of a camera, and the other cylindrical member is a lens support cylinder which is rotatably supported by the cam ring and is moved linearly in an optical axis direction in accordance with the rotation of the cam ring.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-338966 (filed on Nov. 7, 2000) which is expressly incorporated herein by reference in its entirety.